I'm thinking of a character who is cursed (magical in nature) so that everything organic that enters his vision is immediately turned to ash, with the exception of his own body (ie, he won't reduce his own eyelids to ash).
The effects of the curse: When I say "everything organic", I mean everything that is, or once was, living. So the assertion that the character would probably starve is correct, though he would still be able to drink water. He would not extinguish stars by looking at them, nor would he turn the Earth itself into ash (though he could kill any grass and insects on the surface). Since microscopic organisms are, by definition, too small to see, they would be spared from the direct effects of the curse.
If the character only sees part of an organic object, then only the part that he sees will be ashed.
Reflections are more complicated; I was initially going to say that reflections would not trigger the effect, but I need a specific scene where the character uses a coin-operated telescope and sees nothing but devastation.
If I rule out all reflections, then the character would be able to use binoculars without triggering the effect. Similarly, I like the idea of the character seeing a person's reflection in a glass door, but finding nothing but ash when he rushes over to them. So my final ruling for now is that reflections do trigger the effect, unless I can think of a way to consistently allow certain reflections (doors/windows/water), but not others.
Video does not trigger the effect. If he sees something on a live video feed, it will not be destroyed. Though any organic (using my above definition of the word) components of the monitor which are visible from the outside would be destroyed.
Being a magical curse, the process defies the laws of physics by being completely instantaneous and silent. There is no radiation or other energy which is emitted from the character, or the objects turned to ash. The effect covers everything to the very edge of his peripheral vision, and the range extends as far as he can discern (if he uses lenses to view farther, the effect will carry farther).
**Question 1: ** Assuming that this character is an average middle-class person living in a modern city, and the effect just starts when they wake up one morning, how long would it take them to determine that they are the cause of the destruction they now see? What would be the sorts of things that would tip them off?
Question 2: Similarly, what sort of radius of destruction would such a person have (assuming they have average vision)?
EDIT 2: Removed my question about the world's reaction. I'm more specifically curious about the radius of damage that would be caused by a person in this situation.
In a city environment, I would think that people higher up in offices and skyscrapers might be able to look down and see the carnage, while still being far enough from the character's "cone of vision" to be affected by it. However, if they tried to shout a warning at him, he'd instinctively look in their direction, which would instantly kill them.
Any non-artificial fabrics would be instantly destroyed, but I'm thinking that things like dental fillings and surgical implants (ie pacemakers and bone pins/screws) would just drop to the ground, covered in ash, with whatever momentum they still had. I know that car tires would be destroyed, but I'm not sure about paint or ink...ie, whether someone would be able to spray-paint a message for him to see.